package GCB;
/*
    Define the head of a linked list w/wraped entries
        getFirstItem()       returns first entry on the list
        getLastItem()        returns last entry on the list
        setHeadItem(entry)   places entry on the head of the list
        getHeadItem()        returns (and removes) the head of the list
        setTailItem(entry)   places entry on the tail of the list
        getTailItem()        returns (and removes) the tail of the list
        removeItem(entry)    removes the entry from the list
*/
public class ListObjectHead extends ListHead {

//  internal attributes
static final String CODE_FILE = "ListObjectHead";
static final int CODE_REVISION = 2;

//  internal methods
    void display() {
        ListObject e = (ListObject) super.getFirst();
        while(e!=null) {
            Object o = e.getObject();
            System.out.println(o.toString());
            e = (ListObject) e.getNext();
        }
    }

//  external methods
    public ListObjectHead() {super();}       // constructor for object
    public Object getFirstItem() {           // get first entry
        ListObject o = (ListObject) super.getFirst();
        if(o==null) return null;
        return o.getObject();
    }
    public Object getLastItem() {            // get last entry
        ListObject o = (ListObject) super.getLast();
        if(o==null) return null;
        return o.getObject();
    }
    public Object getNextItem(Object o) {
        ListObject e = (ListObject) super.getFirst();
        while(e!=null) {
            if(o==e.getObject()) {
                e = (ListObject) e.getNext();
                if(e!=null) return e.getObject();
                return null;
            }
            e = (ListObject) e.getNext();
        }
        System.out.println(CODE_FILE+
                           " attempt to get next object from wrong list!");
        Thread.dumpStack();
        return null;
    }
    public void setHeadItem(Object o){super.setHead(new ListObject(o));}
    public Object getHeadItem() {
        ListObject o = (ListObject) super.getHead();
        if(o==null) return null;
        return o.getObject();
    }
    public void setTailItem(Object o){super.setTail(new ListObject(o));}
    public Object getTailItem() {
        ListObject o = (ListObject) super.getTail();
        if(o==null) return null;
        return o.getObject();
    }
    public void removeItem(Object o) {
        ListObject e = (ListObject) super.getFirst();
        while(e!=null) {
            if(o==e.getObject()) {
                super.remove(e);
                e.setObject(null);
                return;
            }
            e = (ListObject) e.getNext();
        }
        System.out.println(CODE_FILE+
                           " attempt to remove object from wrong list!");
        Thread.dumpStack();
    }
}